The Light Analysis Render Element provides visual representation of the lighting intensity in the rendered frame. It maps Illuminance and Luminance information as color gradient or a grid of measured values onto the frame. 

The Illuminance and Luminance channels are internally created during rendering. 

During the rendering, the Lighting Analysis might display some approximation to the false-color image, but that is not the final result. After the rendering is finished, you can continue modifying the Lighting Analysis parameters and update the render result in the VFB using the Update button.

Lighting Analysis – Enables the lighting analysis.

Quantity – Chooses which lighting information to be analyzed.

Illuminance (lx) – Uses the Illuminance of the rendered frame in lux.
Luminance (cd) – Uses the Luminance of the rendered frame in candelas.

Min value – Specifies which values are mapped to blue.  

Max value – Specifies which values are mapped to red. 

Scale – Specifies how values are mapped to colors onto the frame. 

Linear – The colors are mapped in linear scale. 
Logarithmic – The colors are mapped in logarithmic scale.  

Display – Specifies the analyzed data display mode. 

False colors –  Fills the frame with a gradient ranging from blue (low values) to red (high values). For the out of range values uses respectively black and white.
Grid overlay – Displays the values at distinct grid points over the frame. They use the same grading colors. 

Grid spacing H/V – Specifies the horizontal/vertical space in pixels between two numeric points on the grid. 

Fade background image – This option is active only if Display is in Grid overlay mode. When enabled, it fades the rendered image, so that the grid values would be more visible.  

Draw legend – When enabled, shows a legend of the false colors at the bottom of the render.  

Update  – Updates the mapped information over the frame if the parameters are changed. V-Ray Frame Buffer must be used for the updates to have effect.